Long curtain rods - Spray paint these babies and you have curtain rods for super cheap! - there is a great idea for easy pinch pleat drapes on this website too.

Attach a sheer curtain panel behind your existing curtains using a bungee cord. Just run the cord through your curtains, attach the bungee hooks to the sides of the rod and stretch it across, and voilà, you have a beautiful sheer inner curtain panel!